This invention relates to a method for treating ink-laden waste water produced from secondary fiber deinking operations. Recycling involves the repulping of used paper to separate the fibers from one another and from the ink, followed by the removal of ink and other extraneous materials from the repulped stock. Various combinations of washing, flotation, and cleaning steps have been used to accomplish this separation. See, for example G. A. Smook, "Handbook for Pulp and Paper Technologists", 7th Edition (1989) pgs. 196 to 201. Additionally, deinking operations utilize various surfactants, along with agents such as caustic soda, silicates and borax to separate ink particles from fiber and to disperse the ink particles in the washing bath. When ink is removed from the paper fibers, ink and surfactant-laden wastewater is produced. It is vital to be able to capture the ink solids from this wastewater prior to discharge.
The wastewater problem has not been adequately solved in the past. Though triazine/aldehyde polymers have many industrial applications, for example in water treatment, paper fiber recovery, decoloration, and in the treatment of the circulating waters of paint spray booths, the use of such polymers in the treatment of wastewater streams generated by deinking operations is not known or suggested in the art.
Canadian Pat. No. 1, 114,079 discloses the use of melamine aldehyde acid colloids in the clarification of water suspensions of finely divided solids, including raw water, raw sewage, and industrial process and wastewaters such as those generated in the coal mining, ore processing and chemical manufacturing industries. The use of these colloids to treat ink-laden wastewater from secondary fiber deinking operations is not disclosed or suggested by this reference.
Copending application U.S. Ser. No. 858,817 relates to the use of a pH-adjustment step in combination with the inorganic and organic coagulants to treat wastewater from a deinking operation.
U.S. Pat. No. 4,656,059 to Mizuno et al relates to the use of melamine-aldehyde acid colloid solutions for treating over sprayed paint captured in spray booths, and U.S. Pat. No. 4,629,572 to Leitz et al relates to the use of urea or amino triazine-aldehyde condensation reaction products in combination with water-swellable clays to treat paint spray booth waters.
Additionally, EP 293129 discloses a method employing melamine aldehyde-type polymers in conjunction with alkalinity sources and flocculant polymers to detackify solvent-based coatings captured in paint spray booth systems. Copending and commonly assigned U.S. patent application Ser. No. 475,670 discloses additional methods for removing solids from water-based paint systems using melamine-aldehyde polymers, and copending and commonly assigned U.S. patent application Ser. No. 588,997 discloses the use of such polymers to treat oversprayed water and solvent-based paint. U.S. Pat. No. 5,068,279 discloses further methods for detackification of paint spray systems using formaldehyde-scavenged melamine formaldehyde polymers. None of these references disclose or suggest the use of melamine aldehyde polymers to treat wastewater generated from a secondary fiber deinking operation.